Bridging the gap between cyclone wind and wave by C‐band SAR measurements

Abstract

AbstractActive microwave remote sensing of hurricane‐strength wind is a challenging task due to the saturation of col‐polarization backscattering signal under such condition. Here we take advantage of the fact that wind sea wave growth does not saturate at high wind and the intrinsic relationship among wind‐wave triplets (sea surface wind speed, significant wave height, and peak wave period) within a tropical storm to derive the wind speed. Three Sentinel‐1 (S‐1) and nine RADARSAT‐2 (R‐2) C‐band synthetic aperture radar (SAR) images acquired between 20 and 40 m/s winds are collected in this study. The S‐1 and R‐2 SAR‐derived winds are compared with those measured by coincident National Oceanic and Atmospheric Administration Stepped‐Frequency Microwave Radiometer (SFMR) and simulated by Symmetric Hurricane Estimates for Wind (SHEW) model. Validations against SFMR winds for S‐1 show Root‐Mean‐Square Error (RMSE) of 1.7 m/s with a 0.2 m/s bias at the left side of cyclone centers and RMSE of 2.9 m/s RMSE with a 0.56 bias at the backside of cyclone centers. R‐2 SAR‐derived winds against SHEW model results show a RMSE of 2.4 m/s with a 0.3 m/s bias and 2.6 m/s with a 0.35 m/s bias at the right side and the left side of cyclone centers, while the RMSE is 3.9 m/s with a 0.1 m/s bias at the backside of cyclone centers. The wave‐information‐based wind retrieval method works well at the left side and right side, but less accurately at the backside of a tropical storm when wind wave and swell are mixed.